Cell wall disruption is an essential downstream processing step for improving the efficiency of lipid extraction from microalgae. Enzyme-assisted extraction of lipid from microalga Scenedesmus sp. ...with cellulase, xylanase and pectinase, using various parameters, such as enzyme concentration, temperature, pH and incubation time, was optimized by central composite design (CCD) coupled with response surface methodology (RSM). Both the lipid extraction from microalgae and the fatty acid methyl esters (FAMEs) production under optimal conditions showed a ∼twofold in the yields compared to the control group with no enzymatic treatment. SEM images, FTIR measurement, XPS and HPLC analysis showed that the enzymatic pretreatment caused significant alterations in the cell wall structure of microalgae. And the disruption of microalgal cell walls was primarily attributed to the breakage of β-glucosidic linkages in cellulose and hemicellulose. The study showed a promising approach can lead to an improvement in the lipid extraction yield from microalgae and further provide valuable information for the use of enzymes in microalgal processes.
•Enzymatic hydrolysis for microalgae cell disruption was studied.•Six process parameters were optimized by respond surface method.•Enzymatic hydrolysis can effectively improve the microalgae biodiesel yield.•Microalgae cell walls were significantly destroyed by multi-enzymes treatment.•The characteristic of cell walls were analyzed by SEM, FTIR, XPS and HPLC.
•Kitchen waste was anaerobically digested at various temperatures and concentrations.•Breakfast, lunch, and dinner kitchen waste were all suitable feedstocks.•Concentrations of 1% and 2% were ...optimal, whereas 4% stopped digestion.•The specific methane yield of dinner is 41.16% higher than the breakfast under optimal condition.•Thermophilic conditions produced more methane than mesophilic conditions.
The anaerobic digestion (AD) performance for breakfast, lunch, and dinner kitchen waste (KW) produced by the canteen at Guangzhou University was assessed by a batch experiment under mesophilic and thermophilic conditions. The AD concentrations were 9.54 g VS/L, 20.12 g VS/L, and 39.99 g VS/L, respectively. The concentration of 20.12 g VS/L under thermophilic conditions had the best AD performance among all the KW. The maximum specific methane yield of 591 ± 30 mL/g VS was obtained from dinner KW (D-KW). Due to the differing organic composition, the specific methane yield of D-KW and lunch KW (L-KW) was 41.16% and 19.76% higher than that of breakfast KW (B-KW) under the optimal condition, respectively, whereas that of D-KW was 17.96% higher than that of L-KW. The specific methane yield was significantly correlated to the crude fat content. When the concentration was increased to 39.99 g VS/L, accumulation of toxic materials was observed and the AD process stopped. The potential biogas yield, based on production of 5904.43 tons of KW per year at the Guangzhou Higher Education Mega Center (HEMC), is 1.08 million m3 biogas, equivalent to 2.15 million KW h of electricity.
To investigate how the changes in performance and the microbial community of the co-digestion system of Pennisetum hybrid and pig manure, two co-digestion systems in a semi-continuous mode were ...established at different grass:manure mixture ratios (50:50 and 75:25), and at variable organic loading rates (OLRs). The two reactors were in a steady-state at the OLRs of 2.0–5.0 g VS/(L·d), with the specific and volumetric biogas yields of 383.86 ± 65.13 to 574.28 ± 72.04 mL/g VS and 0.87 ± 0.07 to 2.36 ± 0.13 m3/(m3·d), respectively. The co-digestion system with a mixture ratio of 75:25 failed at an OLR of 5.5 g VS/(L⋅d). This failure could be attributed to the accumulation of volatile fatty acids (VFAs) owing to the imbalance between acid-production and -oxidation bacteria. By contrast, the co-digestion system with mixture ratio of 50:50 failed at an OLR of 7.0 g VS/(L⋅d), which was likely due to mechanical issues or improper reactor configuration. The genus Proteiniphilum contributed to the increase in total ammonia nitrogen. These findings provide useful guidance for optimizing co-digestion system, enhancing reactor performance and improving the wastes treatment.
•Co-digestion system with 50:50 mixture ratio obtained better stable performance.•Different issues triggered the failure co-digestion process.•Enriched protein-utilizing Proteiniphilum related to the higher ammonia level.•Shift in methanogen could enhance the stability of GP11.
The silage quality of Manyflower silvergrass with microalgae supplementation was investigated, and the variation in bacterial communities during ensilage period was analyzed by high-throughput ...sequencing technology. In addition, the specific methane yields of the silages were also evaluated. Results showed that the samples with microalgae supplementation have lower pH value and higher lactic acid concentration (8.0 mg/g FM). Meanwhile, higher NH3-N concentration was observed since microalgae were N-rich material. Microalgae additions also influenced the bacterial community structure. For the samples without microalgae, the major genus was Enterococcus from day 1 to day 3, and then Lactobacillus became the dominant genus. While the prevalent genus represented in the samples with microalgae supplementation was Lactobacillus. The specific methane yields of all samples were within the range of 153 ± 1 mL/g VS to 178 ± 11 mL/g VS and no significant difference was observed.
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•Improved silage quality was observed with molasses-processed wastewater addition.•Decreased in pH value caused by adding wastewater was the primary factor.•The prevalent genus, ...Lactobacillus, increased by 84% compared to control samples.•The maximum specific methane yield was 259.95±5.75mL/g VS for silage samples.•The Rm value increased by 20.98–56.82% compared to the fresh samples.
The silage quality and anaerobic digestion performance of Pennisetum purpereum with molasses-processed wastewater addition were assessed. The silage samples with molasses-processed wastewater addition obtained higher lactic acid concentration of 15.18–23.38mg/g FM, lower pH value of 3.96–4.45 and lower NH3-N content of 0.47–0.64mg/g FM. No obvious difference was observed in the dominant phyla and genus, but the relative abundance of Lactobacillus reached up to 77.39%, increased by 84% compared to the silage samples without molasses-processed wastewater addition. Combined the silage quality and bacterial community, the decreased in pH value of fresh material caused by molasses-processed wastewater addition was the main reason for improving the silage quality. Meanwhile, the increased in COD concentration is beneficial for improving the specific methane yield and the maximum specific methane yield of 259±5.75mL/g VS was obtained with adding 20g/kg molasses-alcoholic wastewater. Molasses-processed wastewater is an alternative additive for silage.
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•Mono-digestion system of Pennisetum hybrid failed in long-term operation.•The stable organic loading rate (OLR) increased 1-fold by adding bioaugmentation.•Maximum volumetric biogas ...yield of 1.95 m3/(m3·d) obtained at OLR of 4.0 g VS/m3·d.•Dramatically increase in protein- and amino acid-utilizing bacteria observed in R2.•The syntrophism of Syntrophomonas and methanogens has positive effect on stability.
In this study, bioaugmentation with methanogenic propionate-utilizing enrichment was investigated as a method to improve the mono-digestion performance of Pennisetum hybrid in a semi-continuous mode. The effect of bioaugmentation on the microbial community was analyzed as well. The results demonstrate that the steady-state organic loading rate (OLR) of the bioaugmented reactor increased to 4.0 g VS/(L·d) with a volumetric biogas production of 1.95 ± 0.17 m3/(m3·d). In contrast, the non-bioaugmented reactor failed at an OLR of 2.0 g VS/(L·d) accompanied with the accumulation of volatile fatty acids (VFAs). The results of whole genome pyrosequencing analysis suggest that the decrease in relative abundance of syntrophic butyrate and propionate oxidizers, such as Syntrophomonas, Syntrophobacter, and Syntrophorhabdus, reduced the conversion efficiency of butyrate and propionate which leads to the accumulation of butyrate and propionate, influencing the performance of the mono-digestion reactor. Conversely, in the bioaugmented reactor, the higher density of protein- and amino acid-utilizing bacteria, such as Proteiniphilum, Thermovirga, and Lutaonella, as well as the syntrophic association of Syntrophomonas spp. coupled with the methanogens Methanosarcina and Methanocella has a positive effect on system stability and performance.
Anaerobic digestion (AD) technology for rice straw conversion to biogas was investigated for biomass utilization and bioenergy generation. The effects of solid concentration in different temperatures ...on AD efficiency were conducted in bottle-tests, these tests showed that higher biogas production was achieved at the mesophilic temperature. Biogas production was inhibited under thermophilic conditions, and lowest biogas production was achieved in dry thermophilic conditions. According to bottle-test results, the dry AD at ambient condition was selected for 1
m
3 experiment. For pilot-test, the highest methane content, total methane production and methane yield rate were 62%, 9.5
m
3 and 239.7
L/kg VS, respectively. And sour poisoning was effectively avoided by the circulation of leachate. This study could provide useful parameters for the energy utilization of rice straw in South China.
In this study, the links between performance and microbial communities were investigated with municipal solid waste (MSW) at two feedstock ratios and eight organic loading rates (OLRs). The ...co-digestion systems were stably operated at OLRs of 2.0–6.0 g VS/(L·d). The performance of the co-digestion system varied with the feedstock ratio. Compared with the 50:50 (hybrid Pennisetum:MSW) system, the 75:50 system, GM31, obtained increases of 1.93–17.68% and 0.29–23.29% for the specific biogas and methane yields, respectively. Whereas a shift in bacterial and methanogen communities occurred as the operating conditions changed, particularly with OLR variations. The genera Saccharofermentans, Prevotella, Clostridium, Syntrophomonas, and Proteiniphilum became the dominant bacteria for the conversion of carbohydrates and nitrogen compounds as the OLR increased. Meanwhile, a shift from acetoclastic to hydrogenotrophic or multifunctional methanogens was observed.
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